Method for measuring SOC of a battery management system and the apparatus thereof

Abstract

This invention is related to a method and an apparatus for choosing SOCi (State Of Charge based on current) or SOCv (State Of Charge based on voltage) as the SOC (State Of Charge) of a battery depending on a condition in a battery management system by using an equivalent circuit model. In this invention, a method for measuring SOC of a battery in a battery management system is characterized by comprising the steps of: obtaining voltage data and temperature by measuring the current, voltage and temperature of a battery; calculating SOCi by accumulating the current data; calculating open circuit voltage by using an equivalent circuit model which simply presents the current data, the voltage data and the battery through an electric circuit; calculating SOCv by using the temperature data and the open circuit voltage; and choosing at least one of the SOCi and the SOCv as SOC of the battery by using the SOCi and the SOCv based on the judgment on the current state of a vehicle for a certain time interval.

The invention claimed is: 
     
       1. A method for measuring SOC (State Of Charge) of a battery in a battery management system, comprising:
 obtaining, by a battery information obtaining part, current data, voltage data and temperature data by measuring current, voltage and temperature of the battery; 
 calculating, by a current accumulating part, SOCi (State Of Charge based on current) by accumulating the current data; 
 calculating, by a OCV (Open Circuit Voltage) calculating part, OCV using an equivalent circuit model in which the current data, the voltage data and the battery are simply expressed by an electric circuit; 
 estimating, by a SOCv (State Of Charge based on voltage) estimating part, SOCv using the temperature data and the OCV; and 
 judging, by a SOC setting part, a current state of the battery for a desired period of time, and setting up, by the SOC setting part, the SOC of the battery using at least one of the SOCv and the SOCi, 
 wherein the judging of the current state of the battery for the desired period of time, and the setting of the SOC of the battery using at least one of the SOCv and the SOCi, by the SOC setting part, comprises: 
 judging the current state of the battery for the desired period of time, and measuring target SOC of the battery using at least one of the SOCv and the SOCi; 
 calculating ΔSOC which is a difference between the target SOC at a present time and the SOC at a previous time; 
 comparing the ΔSOC with a first critical value; 
 renewing the target SOC at the present time according to a predetermined algorithm and then setting up the renewed target SOC to the SOC of the battery at the present time, if the ΔSOC is larger than the first critical value; and 
 setting up the target SOC at the present time to the SOC of the battery at the present time, if the ΔSOC is not larger than the first critical value, and 
 wherein the algorithm is
   SOC( n +1)=SOC( n )+ΔSOCi+gain X  ΔSOC,
 
 
 −SOC(n+1): SOC of the battery at the present time; 
 −SOC(n): SOC of the battery at the previous time; 
 −ΔSOCi=I(n+1)*Ts/Capa*100%; 
 −(I(n+1) is a current value at the present time, and Ts is a current sampling period, and Capa is a rated capacity of the battery); 
 −0(%/100 msec)<gain<0.1(%/100 msec); and 
 −ΔSOC is a value produced by subtracting the SOC measured at a previous time (n) from the SOC measured at a present time (n+1). 
 
     
     
       2. The method of  claim 1 , wherein the calculating of OCV by the OCV calculating part comprises:
 filtering the current data and the voltage data using a low pass filter; 
 calculating a parameter used in the equivalent circuit model by applying the filtered current data and voltage data to the equivalent circuit model and an adaptive digital filter; and 
 calculating the OCV using the parameter. 
 
     
     
       3. The method of  claim 2 , wherein the low pass filter is a third order low pass filter,
 the equivalent circuit model is expressed by an electric circuit using a resistance parameter R, a current parameter I, a capacitor parameter C, a terminal voltage parameter V and OCV parameter Vo, and 
 the adaptive digital filter continuously renews a value of the parameter used in the equivalent circuit model. 
 
     
     
       4. The method of  claim 1 , wherein the SOCv is set up by the SOC setting part to the SOC of the battery if the battery is in a low current state for the desired period of time, and wherein the SOCi is set up by the SOC setting part to the SOC of the battery if the battery is in other states. 
     
     
       5. The method of  claim 4 , wherein the desired period of time is 20˜60 seconds, and the low current criteria is 2A. 
     
     
       6. The method of  claim 1 , wherein the first critical value is a maximum change value of the SOC per SOC calculation period, and also set up, by the SOC setting part, to various values according to a current limit value. 
     
     
       7. A method for measuring SOC (State Of Charge) of a battery in a battery management system, comprising:
 measuring target SOC of the battery at a present time by measuring current, voltage and temperature of the battery; 
 calculating, by a SOC setting part, ΔSOC which is a difference between the target SOC at the present time and the SOC at a previous time; 
 comparing, by the SOC setting part, the ΔSOC with a first critical value; 
 renewing, by the SOC setting part, the target SOC at the present time according to a predetermined algorithm and then setting up the renewed target SOC to the SOC of the battery at the present time, if the ΔSOC is larger than the first critical value; and 
 setting up, by the SOC setting part, the target SOC at the present time to the SOC of the battery at the present time, if the ΔSOC is not larger than the first critical value, 
 wherein the algorithm is
   SOC( n +1)=SOC( n )+ΔSOCi+gain  X  ΔSOC,
 
 
 −SOC(n+1): SOC of the battery at the present time; 
 −SOC(n): SOC of the battery at the previous time; 
 −ΔSOCi=I(n+1)*Ts/Capa*100%; 
 −(I(n+1) is a current value at the present time, and Ts is a current sampling period, and Capa is a rated capacity of the battery); 
 −0(%/100 msec)<gain<0.1(%/100 msec); and 
 −ΔSOC is a value produced by subtracting the SOC measured at a previous time (n) from the SOC measured at a present time (n+1). 
 
     
     
       8. The method of  claim 7 , wherein the measuring of the target SOC of the battery at the present time by measuring current, voltage and temperature of the battery comprises:
 obtaining, by a battery information obtaining part, current data, voltage data and temperature data by measuring the current, voltage and temperature of the battery; 
 calculating, by a current accumulating part, SOCi (State Of Charge based on current) by accumulating the current data; 
 calculating, by a OCV (Open Circuit Voltage) calculating part, OCV using an equivalent circuit model in which the current data, the voltage data and the battery are simply expressed by an electric circuit; 
 estimating, by a SOCv (State Of Charge based on voltage) estimating part, SOCv using the temperature data and the OCV; and 
 judging, by the SOC setting part, a current state of the battery for a desired period of time, and setting up, by the SOC setting part, the SOC of the battery using at least one of the SOCv and the SOCi. 
 
     
     
       9. The method of  claim 7 , wherein the first critical value is a maximum change value of the SOC per SOC calculation period, and also set up to various values according to a current limit value. 
     
     
       10. A battery management system, comprising:
 a battery information obtaining part that measures current, voltage and temperature of the battery and obtains current data, voltage data and temperature data; 
 a current accumulating part that calculates SOCi by accumulating the current data; 
 a OCV calculating part that calculates OCV using an equivalent circuit model in which the current data, the voltage data and the battery are simply expressed by an electric circuit; 
 a SOCv estimating part that estimates SOCv using the temperature data and the OCV; and 
 a SOC setting part that judges a current state of the battery for a desired period of time, and sets up the SOC of the battery using at least one of the SOCv and the SOCi, wherein the SOC setting part judges a current state of the battery for a desired period of time and measures target SOC of the battery using at least one of the SOCi and SOCv; calculates ΔSOC which is a difference between the target SOC at the present time and the SOC at a previous time; compares the ΔSOC with a first critical value; renews the target SOC at the present time according to a predetermined algorithm and then setting up the renewed target SOC to the SOC of the battery at the present time if the ΔSOC is larger than the first critical value; and sets up the target SOC at the present time to the SOC of the battery at the present time if the ΔSOC is not larger than the first critical value, and 
 wherein the algorithm is
   SOC( n +1)=SOC( n )+ΔSOCi+gain X ΔSOC,
 
 
 −SOC(n+1): SOC of the battery at the present time; 
 −SOC(n): SOC of the battery at the previous time; 
 −ΔSOCi=I(n+1)*Ts/Capa*100%; 
 −(I(n+1) is a current value at the present time, and Ts is a current sampling period, and Capa is a rated capacity of the battery); 
 −0(%/100 msec)<gain<0.1(%/100 msec); and 
 −ΔSOC is a value produced by subtracting the SOC measured at a previous time (n) from the SOC measured at a present time (n+1). 
 
     
     
       11. The battery management system of  claim 10 , further comprising a low pass filtering part that filters the current data and the voltage data using a low pass filter,
 wherein the OCV calculating part applies the current data and the voltage data filtered by the low pass filtering part to the equivalent circuit model and an adaptive digital filter, calculates a parameter used in the equivalent circuit model and then calculates the OCV using the parameter. 
 
     
     
       12. The battery management system of  claim 11 , wherein the low pass filter is a third order low pass filter,
 the equivalent circuit model is expressed by an electric circuit using a resistance parameter R, a current parameter I, a capacitor parameter C, a terminal voltage parameter V and OCV parameter Vo, and 
 the adaptive digital filter renews a value of the parameter using in the equivalent circuit model, continuously. 
 
     
     
       13. The battery management system of  claim 10 , wherein the SOCv is set up to the SOC of the battery if the battery is in a low current state for the desired period of time, and wherein the SOCi is set up to the SOC of the battery if the battery is in other states. 
     
     
       14. The battery management system of  claim 13 , wherein the desired period of time is 20˜60 seconds, and the low current criteria is 2A. 
     
     
       15. The battery management system of  claim 10 , wherein the first critical value is a maximum change value of the SOC per SOC calculation period, and also set up to various values according to a current limit value.